support down to py3.9, bump version

Author: DavidBuchanan314

.github/workflows/test.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [ '3.11', '3.12', '3.13' ]
+        python-version: [ '3.9', '3.10', '3.11', '3.12', '3.13' ]
     name: Python ${{ matrix.python-version }} tests
     steps:
       - uses: actions/checkout@v4

pyproject.toml

@@ -6,13 +6,13 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "atmst"
-version = "0.0.3"
+version = "0.0.4"
 authors = [
  	{ name="David Buchanan", email="d@vidbuchanan.co.uk" },
 ]
 description = "A Python library for wrangling atproto-flavoured Merkle Search Trees"
 readme = "README.md"
-requires-python = ">=3.11"
+requires-python = ">=3.9"
 classifiers = [
 	"Programming Language :: Python :: 3",
 	"License :: OSI Approved :: MIT License",

src/atmst/mst/node.py

@@ -4,7 +4,10 @@
 from more_itertools import ilen
 from itertools import takewhile
 from dataclasses import dataclass
-from typing import Tuple, Self, Optional
+
+from typing import TYPE_CHECKING, Tuple, Optional
+if TYPE_CHECKING: # Self doesn't exist <3.11
+	from typing import Self
 
 from cbrrr import encode_dag_cbor, decode_dag_cbor, CID
 
@@ -38,7 +41,7 @@ def __post_init__(self) -> None:
 			raise ValueError("Mismatched keys/vals lengths")
 
 	@classmethod
-	def empty_root(cls) -> Self:
+	def empty_root(cls) -> "Self":
 		return cls(
 			subtrees=(None,),
 			keys=(),
@@ -78,7 +81,7 @@ def serialised(self) -> bytes:
 		})
 
 	@classmethod
-	def deserialise(cls, data: bytes) -> Self:
+	def deserialise(cls, data: bytes) -> "Self":
 		cbor = decode_dag_cbor(data)
 		if len(cbor) != 2: # e, l
 			raise ValueError("malformed MST node")

src/atmst/mst/node_walker.py

@@ -1,5 +1,7 @@
 from dataclasses import dataclass
-from typing import Tuple, Self, Optional, List, Iterable
+from typing import TYPE_CHECKING, Tuple, Optional, List, Iterable
+if TYPE_CHECKING: # Self doesn't exist <3.11
+	from typing import Self
 
 from cbrrr import CID
 
@@ -45,7 +47,7 @@ def __init__(self, ns: NodeStore, root_cid: Optional[CID], lpath: Optional[str]=
 			idx=0
 		)]
 
-	def subtree_walker(self) -> Self:
+	def subtree_walker(self) -> "Self":
 		return NodeWalker(self.ns, self.subtree, self.lpath, self.rpath)
 
 	@property